One of the most common choices for a solar system science fair project is a model of the solar system. A model can focus on recreating the colors of each planet or can focus more on creating a scale model. Scale models can become very large, however, because of the vast distances between the planets.
For children who want to study the solar system, they can create a project around solar flares. Students can study how solar flares affect radio signals or various technologies in use today. Students can also map out solar flare activity. When studying solar flare effects, it is a good idea to study the technology while solar flares are happening and when they are not. This will provide a control for the experiment.
Similar to studying solar flares, students can also study solar storms and how they affect things in our world. A student could figure out how to predict solar storms or how they affect satellites or radio transmissions. Students could also study the different types of solar storms and present a comprehensive project that explains the differences.
Since each planet in the solar system has a different atmosphere, students can also create a science fair project that compares them. A student could focus on why Earth supports life and the others planets do not or they might pick one planet and describe the atmosphere of that planet in detail. A student could also compare gas planets to non-gaseous planets and describe the basic differences between them.